The Japanese government has pledged to shoot down any debris that falls over its territory.

To me, that sounds strange. The only way I can see in which this would help is if they manage to break the debris into many pieces before it slows down into the atmosphere, so that parts may be small enough to burn up completely. If they manage to shoot it down later, they can at best replace a few large pieces of launcher debris to a large number of small pieces of launcher debris and missile debris. My questions:

What causes more damage:

A small number of large pieces of launcher debris?

A large number of small pieces of launcher debris + debris from the missile used to destroy this debris?

Is there any historical precedent of shooting down debris from a satellite launch?

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I'm afraid this is more of a politics questions than a physics one, the main reason the Japanese are preparing to intercept the rocket (or its debris) if it approaches their territory is that they aren't convinced the North Korean launch is a peaceful one.
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YannisDec 7 '12 at 9:20